A. Yu. Snegirev

The large eddy simulation of a turbulent diffusion flame

Internal structure of a turbulent diffusion flame (Sandia Flame D) has been investigated numerically by means of CFD code Ansys Fluent 6.3. For this flame, detailed measurements are currently available. In the simulations, two strategies of turbulence modeling (large eddy simulation and Reynolds-Favre averaging) jointly with two approaches to model turbulent combustion (the mixture fraction probability density function model and the eddy dissipation model) have been applied. Comparisons of the simulation results with the available measurement data made it possible to identify the most adequate methodology for modeling turbulent diffusion jet flame.

Simultaneous self-focusing of two laser beams in a subthreshold coherent population trapping regime

The propagation of two-component laser radiation in a medium consisting of atoms with a Λ level scheme is investigated. The simultaneous self-focusing of two beams is considered. The main features of this phenomenon are: 1) lowering of the self-focusing threshold by several orders of magnitude in comparison with the known case of saturation of a transition in a two-level atom; 2) a strong dependence of the character of the propagation of the radiation on the difference between the detunings of the two frequency components of the field from resonance, which is associated with fulfillment of the two-photon resonance condition.

Natural Buoyant Turbulent Diffusion Flame near a Vertical Surface

The structure and dynamics of a natural buoyant turbulent diffusion flame near a vertical surface with combustible gas exhaustion are numerically studied by using the FDS model and computer code. The flame is considered near the surface through which gaseous propylene is injected with a prescribed flow rate. Requirements are determined for the grid cell size in the near-wall region, which ensure sufficient spatial resolution of the boundary layer structure. It is shown that the predicted value of the total heat flux at the surface agrees with the measured results. Investigations of ignition and combustion of a vertical plate of non-charring thermoplastic (polymethylmetacrylate) with allowance for the material pyrolysis reaction show that the ignitor parameters determine the duration of the transient period, but weakly affect the growth of the heat release rate and the height of the pyrolysis region at the stage of developed burning. Significant effects of the ignitor shape, size, and temperature, as well as lateral entrainment of air on the velocity of the upward flame spread rate over the plate surface and on the shape of the pyrolysis front are revealed. The existence of critical parameters of the ignitor separating flame decay from developed burning is demonstrated. Three flame spread regimes with different pyrolysis front shapes are identified.

Erratum to: “Natural Buoyant Turbulent Diffusion Flame near a Vertical Surface”

In the original publication, the title was misspelled. It should read “Buoyant Turbulent Diffusion Flame near a Vertical Surface ” instead of “Natural Buoyant Turbulent Diffusion Flame near a Vertical Surface.”It should also read “buoyant turbulent diffusion flame” instead of “natural buoyant turbulent diffusion flame” everywhere else in the text and “the upward flame spread rate” instead of “the velocity of the upward flame spread rate” in the abstract.The original Russian text was translated by the journal.

Cooperative population dynamics of an ensemble of Λ atoms in a bichromatic field

Equations are derived which describe the dynamics of three-level atoms with a Λ level scheme, interacting with two coherent resonance fields under conditions such that cooperative relaxation predominates over incoherent spontaneous emission. A numerical calculation of the temporal dynamics of the values of the atomic populations is performed. It is shown that coherent population trapping in the presence of cooperative decay is possible. The quantities characterizing this phenomenon are calculated—the width of the black line and the transition time to coherent trapping in this scheme.

Determination of kinetic parameters for a pyrotechnic mixture

A general approach is considered to covering formally kinetic parameters from experiments for ignition, firing, or combustion of condensed substances based on minimizing discrepancies in experimental and calculated values. Results are provided for determining kinetic constants of a pyrotechnic mixture from data of firing it by a heated surface at a constant temperature.